Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$217.55	6.282%	$231.2165	$231.22	$231.20	$231.20
Purchase #2	$129.61	11.613%	$144.6616	$144.66	$144.65	$144.70
Purchase #3	$90.78	4.117%	$94.5174	$94.52	$94.50	$94.50
Purchase #4	$144.57	5.715%	$152.8322	$152.83	$152.85	$152.80
Purchase #5	$104.36	10.167%	$114.9703	$114.97	$114.95	$115.00
Purchase #6	$31.49	6.597%	$33.5674	$33.57	$33.55	$33.60
Purchase #7	$100.26	5.583%	$105.8575	$105.86	$105.85	$105.90
7 purchase totals =	$818.62		$877.6229	$877.63	$877.55	$877.70